4,603 research outputs found
Boundary Shape and Casimir Energy
Casimir energy changes are investigated for geometries obtained by small but
arbitrary deformations of a given geometry for which the vacuum energy is
already known for the massless scalar field. As a specific case, deformation of
a spherical shell is studied. From the deformation of the sphere we show that
the Casimir energy is a decreasing function of the surface to volume ratio. The
decreasing rate is higher for less smooth deformations.Comment: 12 page
Single scale factor for the universe from the creation of radiation and matter till the present
A scheme for incorporating the creation of radiation and matter into the
cosmological evolution is introduced so that it becomes possible to merge the
times before and after the creation of radiation and matter in a single scale
factor in Robertson-Walker metric. This scheme is illustrated through a toy
model that has the prospect of constituting a basis for a realistic model.Comment: Minor typos are corrected, an acknowledgment is added, to be
published in The European Physical Journal
Higgsed Stueckelberg Vector and Higgs Quadratic Divergence
Here we show that, a hidden vector field whose gauge invariance is ensured by
a Stueckelberg scalar and whose mass is spontaneously generated by the Standard
Model Higgs field contributes to quadratic divergences in the Higgs boson mass
squared, and even leads to its cancellation at one-loop when Higgs coupling to
gauge field is fine-tuned. In contrast to mechanisms based on hidden scalars
where a complete cancellation cannot be achieved, stabilization here is
complete in that the hidden vector and the accompanying Stueckelberg scalar are
both free from quadratic divergences at one-loop. This stability, deriving from
hidden exact gauge invariance, can have important implications for modelling
dark phenomena like dark matter, dark energy, dark photon and neutrino masses.
The hidden fields can be produced at the LHC.Comment: 5pp, 1 fig. Improved exposition, rectified concurrency to broken and
unbroken electroweak vacua, added reference
Finite-parameter feedback control for stabilizing the complex Ginzburg-Landau equation
In this paper, we prove the exponential stabilization of solutions for
complex Ginzburg-Landau equations using finite-parameter feedback control
algorithms, which employ finitely many volume elements, Fourier modes or nodal
observables (controllers). We also propose a feedback control for steering
solutions of the Ginzburg-Landau equation to a desired solution of the
non-controlled system. In this latter problem, the feedback controller also
involves the measurement of the solution to the non-controlled system.Comment: 20 page
Directed Growth of Hydrogen Lines on Graphene: High Throughput Simulations Powered by Evolutionary Algorithm
We set up an evolutionary algorithm combined with density functional
tight-binding (DFTB) calculations to investigate hydrogen adsorption on flat
graphene and graphene monolayers curved over substrate steps. During the
evolution, candidates for the new generations are created by adsorption of an
additional hydrogen atom to the stable configurations of the previous
generation, where a mutation mechanism is also incorporated. Afterwards a
two-stage selection procedure is employed. Selected candidates act as the
parents of the next generation. In curved graphene, the evolution follows a
similar path except for a new mechanism, which aligns hydrogen atoms on the
line of minimum curvature. The mechanism is due to the increased chemical
reactivity of graphene along the minimum radius of curvature line (MRCL) and to
sp bond angles being commensurate with the kinked geometry of hydrogenated
graphene at the substrate edge. As a result, the reaction barrier is reduced
considerably along the MRCL, and hydrogenation continues like a mechanical
chain reaction. This growth mechanism enables lines of hydrogen atoms along the
MRCL, which has the potential to overcome substrate or rippling effects and
could make it possible to define edges or nanoribbons without actually cutting
the material.Comment: 10 pages of main text, 37 pages of supplementary information, 1
supplementary vide
Characteristic Energy of the Coulomb Interactions and the Pileup of States
Tunneling data on crystals confirm
Coulomb interaction effects through the dependence of the
density of states. Importantly, the data and analysis at high energy, E, show a
pileup of states: most of the states removed from near the Fermi level are
found between ~40 and 130 meV, from which we infer the possibility of universal
behavior. The agreement of our tunneling data with recent photoemission results
further confirms our analysis.Comment: 4 pages, 4 figures, submitted to PR
Tevatron Higgs Mass Bounds: Projecting U(1)' Models to LHC Domain
We study Higgs boson masses in supersymmetric models with an extra U(1)
symmetry to be called U(1). Such extra gauge symmetries are urged by
the problem of the MSSM, and they also arise frequently in low-energy
supersymmetric models stemming from GUTs and strings. We analyze mass of the
lightest Higgs boson and various other particle masses and couplings by taking
into account the LEP bounds as well as the recent bounds from Tevatron
experiments. We find that the -problem motivated generic low-energy
U(1) model yields Higgs masses as large as and
violate the Tevatron bounds for certain ranges of parameters. We analyze
correlations among various model parameters, and determine excluded regions by
both scanning the parameter space and by examining certain likely parameter
values. We also make educated projections for LHC measurements in light of the
Tevatron restrictions on the parameter space. We further analyze certain
benchmark models stemming from E(6) breaking, and find that they elevate Higgs
boson mass into Tevatron's forbidden band when U(1) gauge coupling
takes larger values than the one corresponding to one-step GUT breaking.Comment: 11 pages, 3 figure
Semi-classical black holes with large N re-scaling and information loss problem
We consider semi-classical black holes and related re-scalings with N
massless fields. For a given semi-classical solution of an N = 1 universe, we
can find other solution of a large N universe by the re-scaling. After the
re-scaling, any curvature quantity takes a sufficiently small value without
changing its causal structure. Via the re-scaling, we argue that black hole
complementarity for semi-classical black holes cannot provide a fundamental
resolution of the information loss problem, and the violation of black hole
complementarity requires sufficiently reasonable amounts of N. Such N might be
realized from some string inspired models. Finally, we claim that any
fundamental resolution of the information loss problem should resolve the
problem of the singularity.Comment: 33 pages, 5 figure
Higher Curvature Quantum Gravity and Large Extra Dimensions
We discuss effective interactions among brane matter induced by modifications
of higher dimensional Einstein gravity via the replacement of Einstein-Hilbert
term with a generic function f(R) of the curvature scalar R. After deriving the
graviton propagator, we analyze impact of virtual graviton exchanges on
particle interactions, and conclude that f(R) gravity effects are best probed
by high-energy processes involving massive gauge bosons, heavy fermions or the
Higgs boson. We perform a comparative analysis of the predictions of f(R)
gravity and of Arkani-Hamed-Dvali-Dimopoulos (ADD) scenario, and find that the
former competes with the latter when f''(0) is positive and comparable to the
fundamental scale of gravity in higher dimensions. In addition, we briefly
discuss graviton emission from the brane as well as its decays into
brane-localized matter, and find that they hardly compete with the ADD
expectations. Possible existence of higher-curvature gravitational interactions
in large extra spatial dimensions opens up various signatures to be confronted
with existing and future collider experiments.Comment: 19 pp, 2 figs. Added references, corrected typo
LEP Indications for Two Light Higgs Bosons and U(1)' Model
Reanalyses of LEP data have shown preference to two light CP-even Higgs
bosons. We discuss implications of such a Higgs boson spectrum for the minimal
supersymmetric model extended by a Standard Model singlet chiral superfield and
an additional Abelian gauge invariance (the U(1)' model). We, in particular,
determine parameter regions that lead to two light CP-even Higgs bosons while
satisfying existing bounds on the mass and mixings of the extra vector boson.
In these parameter regions, the pseudoscalar Higgs is found to be nearly
degenerate in mass with either the lightest or next-to-lightest Higgs boson.
Certain parameters of the U(1)' model such as the effective mu parameter are
found to be significantly bounded by the LEP two-light-Higgs signal.Comment: 20 pp, 7 figs, 2 table
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